The present invention relates to the field of paint mixers of the type for mixing paint and related liquid coatings in conventional containers in the range of about 5 gallons or about 20 liters. More particularly, the present invention relates to such mixers which utilize gyroscopic mixing motion while the coating container is clamped between a pair of opposed plates. It is to be understood that such mixers are suitable for mixing coatings in the range of about 1 gallon to about 5 gallons (or the metric equivalent), and may be utilized to mix coatings in other than cylindrical containers, including, but not limited to so-called “square” containers, particularly when adapters or special shaped container holders are used.
In the past, one such mixer clamped the coating container by advancing one plate towards the other using a lead screw rotated by a hand wheel. While such an approach was generally satisfactory, the lead screw was prone to unscrewing during mixing, resulting in unintended partial or full release of the coating container, with consequent damage to the coating container and possibly the mixer. If the coating container was breached during such release, the coating would typically spill, contaminating the mixer and possibly the environment of the mixer. Such a result is naturally undesirable.
The present invention overcomes the shortcoming of the above described prior art mixer by providing a locking clamp for a gyroscopic type paint mixer which prevents the unintended release of the opposed plate clamp.
In another aspect, the above described prior art machine had a single traveling clamping screw attached to a handle and threaded through a stationary nut. Rotating the handle turned the screw and resulted in an axial displacement of the screw. In this prior art machine, the top clamping plate was attached to the screw and thus traveled up and down to clamp and unclamp the paint container.
The present invention also uses a single lead screw. However, in the present invention, the screw can rotate but is axially fixed. In the present invention, the screw is threaded through a nut which is free to travel axially but is fixed against rotation by rigidly mounting it to a cross member or bridge portion captured between two upright members or portions. By fixing the nut against rotation in the present invention (i.e. not allowing the nut to turn with the lead screw), the nut travels up and down when the screw is rotated, thus moving the top clamp plate to clamp and unclamp the paint container.
Another prior art gyroscopic type mixer used twin lead screws and two or more upright supports. In that prior art machine, turning the crank handle engaged a series of gears which rotated the twin lead screws. The lead screws were free to rotate but were fixed axially. The clamp plates were attached to cross-members that had threaded nuts fixed against rotation. In that prior art machine, turning the lead screws caused both the top and bottom clamp plates to move towards or away from each other to clamp or unclamp a paint container, in contrast to the present invention which moves only the top plate. The prior art machine which moves both plates simultaneously tended to keep the center of mass close to the tumble axis. In contrast, one aspect of the present invention permanently positions the center of mass below the tumble axis, allowing gravity to urge the rotating frame and paint container to stop in an upright position. Furthermore, the present invention greatly simplifies the design by requiring fewer parts in series in the clamping mechanism, with consequent reduction in cost and friction between operating parts.
Other aspects of the present invention include at least one splash guard for each range-of-travel portion for the movable part or parts of the clamping mechanism to prevent contamination with consequent increase in friction. A flange on the splash guard also acts as a stop to limit motion of the movable parts of the clamping mechanism at an end of the range-of-travel. In addition, the present invention includes at least one corresponding guide member to maintain the relationship between the fixed and moving parts of the rotatable clamp apparatus, with the guide member(s) formed of a polymer to reduce friction. Another aspect of the present invention is a strike plate located below a guide roller at a lower edge of a front opening of the mixer. The strike plate prevents the roller from denting the paint container as it is removed from the mixer, particularly when the container is metal. A still further aspect of the present invention is a relief formed in a raised lip on the lower clamp plate to aid in the transfer of the paint container into and out of the clamping apparatus. Yet another aspect of the present invention is to have a common base on which both a stationary sun gear and a planet gear (on the rotating clamp) are rigidly mounted, eliminating the play present with one prior art mixer design in which vibration mounts allowed the planet gear to “float” with respect to the sun gear, causing excessive misalignment and wear.